Parathyromatosis, in which several nodules of hyperfunctioning parathyroid tissue form in the neck and mediastinum, is a rare cause of recurrent hyperparathyroidism. However, there are some theories regarding the origin of parathyromatosis, and seeding after rupture of the parathyroid gland capsule during surgical removal of a parathyroid lesions is the most regarded one. Herein, we report a 41-year-old man who presented with multiple parathyroid nodules in and around the left thyroid lobe 5 years after parathyroid surgery for secondary hyperparathyroidism that was finally diagnosed as parathyromatosis. We discuss the differential diagnosis of parathyromatosis from other parathyroid tumors, particularly from parathyroid carcinoma, which is important in the management of a suspected lesion. © 2012 The Korean Society of Pathologists/The Korean Society for Cytopathology.